1. Field of Invention:
The present invention relates to a charge coupled device (referred to CCD hereinafter), particularly to the structure of an output portion thereof for detecting and outputting a signal electric charge.
2. Description of the Related Art
There are a Floating Diffusion method (referred to FD method hereinafter) and a Floating Gate method (referred to FG method hereinafter) in the signal output methods of the CCD. The FD method detects the change of electric potential which is generated when a signal electric charge is applied to a reverse bias on a junction capacitance. The FG method detects the change of electric potential of a MOS gate electrode when a signal electric charge is applied to the capacitance when the floating MOS gate electrode is floating.
The FG method generates little noise at a detecting portion for detecting the signal electric charge. Moreover, the FG method can detect the signal electric charge without deteriorating the same, so that the FG method can reuse the detected signal. Accordingly, the FG method is used as a very effective means when a plurality of signal detections are required using a same signal. For example, the FG method is used in a CCD camera element which needs a high S/N ratio (signal/noise ratio), a CCD delay line, or a CCD filter element.
Such a CCD is disclosed, for example, in the Japanese Laid-Open Patent Publication No. 3-19349, published on Jan. 28, 1991 or the Japanese Laid-Open Patent Publication No. 61-220467, published on Sep. 30, 1986.